Investigation On The Dynamic Compositional Changes Of Yeast RPL36 Paralog-specific Ribosomes In Response To Physiological Adjustment And Its Effects On Translational Regulation

Traditionally,ribosomes were considered as translational machinery with constant composition and well-defined function.However,recent studies have indicated existence of many ribosomal composition variants in organisms ranging from bacteria to human.In addition,ribosomes with distinct composition and/or modifications have also been observed during differentiation,at different stages of development,and in various tissues.These findings raise a possibility that ribosomes might actively participate in the regulation of protein production.In haploid yeast cells,among the 78 core ribosomal proteins,there are 59 pairs of ribosomal protein paralogs.Previous study demonstrated that ribosomes assembled from one of a pair of ribosomal protein paralogs exhibit differential functions from ribosomes assembled with the other paralog.Therefore,theoretically,there might be 259 different types of ribosomes in yeast.Yet,the mechanism underlying the functional differentiation between the two ribosomal protein paralogs and the definitive proof to validate existence of different types of ribosomes in the same cell have not been resolved.By introducing the two endogenous yeast RPL36 paralogs with different tags,combined with sucrose density centrifugation,followed by sequential immunoprecipitation,we were able to cleanly purify the two RPL36 paralog-specific ribosomes.Mass spectrometric analysis proves the two paralog-specific ribosomes indeed harbor distinct composition.Based on our previous finding,this proposal aims to further delineate the functions of the paralog-specific ribosomes,to find out the particular subset of mRNAs preferentially bound by each type of paralog-specific ribosomes,to determine if the composition of the ribosomes will change with physiological conditions,and to assess whether change in ribosomal composition in response to physiological condition correlates with reprogramming of the translated mRNAs.